What is the best definition of an RTOS? -


i have yet find definition of rtos specific enough have meaning. best 1 can find on wiki:

https://en.wikipedia.org/wiki/real-time_operating_system

however have critical comments/questions:

  1. "real time" seems undefined in definitions rtos i've found. nothing can fast actual real time (infinitesimally small!). therefore, believe "real time" makes sense in context of observer. real time human using iphone user might <20ms because human eye sight cannot detect changes faster that. air bag deployment might <1ms. definitions on internet seem gloss on definition of "real time"!

  2. if rtos defined requirement execute within specific time frame ("deadline"), why jitter come definition? if iphone response jitters between 12-14ms, no longer responding in real time? meets 20ms requirement, right? if 1 time response went 100ms, user might notice, @ point system not rtos
  3. how can there possibly "soft" rtos?! definition of rtos meeting particular deadline time requirement. if doesn't meet it, not rtos! definition of rtos prohibits "soft" rtos

to me seems there no formal , precise definition of rtos. it's general term explain characteristic of os who's main priority appearance of "real time" (per requirement number) particular type of observer. seems name has taken on implementation meaning such how things processed, multi-tasking, message passing, semaphores, etc... may not part of rtos @ if system fails respond within "deadline" requirement, right?

sorry such ubiquitous question, can't clear picture in brain. definitions i've found not precise enough or cloud definition implementation details.

there embedded systems dictionary. here excerpts:

real-time adj. having timeliness requirements, typically in form of deadlines can’t missed.

real-time operating system n. operating system designed use in real-time systems. abbreviated rtos.

real-time system n. computer system, embedded or otherwise, has timeliness requirements. following question can used distinguish real-time systems rest: “is late answer bad, or worse, wrong answer?” in other words, happens if computation doesn’t finish in time? if nothing bad happens, it’s not real-time system. if dies or mission fails, it’s considered “hard” real-time, meant imply system has hard deadlines. in between “soft” real-time.


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